Substitution call control system in a communication network

ABSTRACT

A substitution call control system includes an ATM (Asynchronous Transfer Mode) subscriber network of an ATM communication network. The ATM subscriber network includes a plurality of network terminators respectively connected with a plurality of subscriber terminals, and an ATM subscriber line concentrator, which accommodates VCs (Virtual Connection) to the plurality of network terminators, and is connected with a ATM switching apparatus of the ATM network through a UNI (User-Network Interface). The ATM subscriber line concentrator includes a substitution call control function to substitute for the plurality of network terminators and the subscriber terminals for a call control.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/324,655 filed Jun. 3, 1999, now U.S. Pat. No. 6,859,457 thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a call control in an ATM (AsynchronousTransfer Mode) subscriber communication network. More particularly, thepresent invention relates to a substitution call control system whichsubstitutes a call control from a subscriber terminal in an ATM lineconcentrator.

2. Description of the Related Art

There are PVC (Permanent Virtual Channel) and SVC (Switched VirtualChannel) in an ATM communication network, and the establishment andrelease of a SVC connection is controlled.

As protocol for the control of establishment and release of the SVCconnection, the following protocols are used. That is, they are:

ITU-T recommendation Q.2110 (to be referred to as SSCOP hereinafter),

ITU-T recommendation Q.2130 (to be referred to as SSCF hereinafter),

ITU-T recommendation Q.2931 and ITU-T recommendation Q.2971,

ATM Forum Technical Committee ATM UNI (User-Network Interface)Specification Version 3.1 (to be referred to as UNI3.1 hereinafter), and

ATM Forum Technical Committee ATM UNI Signaling Specification Version4.0(to be referred to as UNI4.0 hereinafter) with respect to a signalinglayer.

FIG. 1 is a block diagram illustrating a conventional call controlsystem of an ATM communication system. In FIG. 1, an ATM subscribernetwork 11 is connected with an ATM switching apparatus 20 of an ATMnetwork 10 through a UNI (User-Network Interface) 12. The ATM subscribernetwork 11 is composed of an ATM subscriber line concentrator 30, and aplurality of network terminators 40 a to 40 c. The ATM subscriber lineconcentrator 30 accommodates the plurality of network terminators 40 ato 40 c. Each of a plurality of subscriber terminals 50 a to 50 c isconnected with a corresponding one of the network terminators 40 a to 40c.

In the conventional call control system, a call control function 100 ais installed in the ATM switching apparatus 20 of the ATM network 10.Call control functions 100 b and 10 c are installed in each of the ATMsubscriber line concentrator 30 and the network terminators 40 a to 40 cin the ATM subscriber network 11. Also, call control functions 100 d areinstalled in the subscriber terminals 50 a to 50 c. Thus, theflexibility and effective usage of the allocation of network resourcesin the ATM network 10 and the ATM subscriber network 11 are intended.

FIG. 2 is a diagram illustrating protocols used to realize theconventional call control functions 100 a to 100 d shown in FIG. 1. InFIG. 2, the ATM switching apparatus 20 in the ATM network 10 is composedof a SDH layer 110 a, an ATM layer 111 a, an AAL5 layer 112 a, an SSCOPlayer 113 a, an SSCF layer 114 a, a signaling layer 115 a and an ATMswitching apparatus application 130.

The ATM subscriber line concentrator 30 has two layer structures and anATM subscriber line concentrator application 140. One of the two layerstructures is composed of a SDH layer 110 b, an ATM layer 111 b, an AAL5layer 112 b, an SSCOP layer 113 b, an SSCF layer 114 b, a signalinglayer 115 b, and the other is composed of a SDH layer 110 c, an ATMlayer 111 c, an AAL5 layer 112 c, an SSCOP layer 113 c, an SSCF layer114 c, a signaling layer 115 c.

Each of the network terminators 40 a to 40 c has two layer structuresand a network terminator application 150. One of the two layerstructures is composed of a SDH layer 110 d, an ATM layer 111 d, an AAL5layer 112 d, an SSCOP layer 113 d, an SSCF layer 114 d, a signalinglayer 115 d, and the other is composed of a SDH layer 110 e, an ATMlayer 111 e, an AAL5 layer 112 e, an SSCOP layer 113 e, an SSCF layer114 e, a signaling layer 115 e.

Each of the subscriber terminals 50 a to 50 c is composed of a SDH layer110 f, an ATM layer 111 f, an AAL5 layer 112 f, an SSCOP layer 113 f, anSSCF layer 114 f, a signaling layer 115 f and a subscriber-terminalapplication 160.

As described above, the protocol of each of the call control functions100 a to 100 d is composed of:

the physical layer (SDH: Synchronous Digital Hierarchy) 110 a to 110 f,

the ATM layer 111 a to 111 f defined by ITU-T recommendation I.361,

the AAL5 layer (AAL: ATM Adaptation Layer) 112 a to 112 f defined byITU-T recommendation I.363,

the SSCOP layer 113 a to 113 f defined by ITU-T recommendation Q.2110,

the SSCF layer 114 a to 114 f defined by ITU-T recommendation Q.2130,and

the signaling layer 115 a to 115 f for executing a call control.

The ATM switching apparatus 20 is provided with an ATM switchingapparatus application 130 which controls the call control protocol. TheATM subscriber line concentrator 30 is provided with an ATM subscriberline concentrator application 140 which controls the call controlprotocol. Each of the network terminators 40 a to 40 c is provided witha network terminator application 150 and each of the subscriberterminals 50 a to 50 c is provided with a subscriber terminalapplication 160.

Next, the operations of the call control functions shown in FIG. 1 willbe described.

A call control procedure is executed between the call control functions10 a of the ATM switching apparatus 20 and the call control function 100b of the ATM subscriber line concentrator 30 through a channel 210 a ofVPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier)=VPidentifier/VC identifier=0/5 defined in UNI 3.1 by UNI 12. Thus, theestablishment and release of a SVC connection 200 a between the ATMswitching apparatus 20 and the ATM subscriber line concentrator 30 iscontrolled.

A call control procedure is executed between the call control function100 b of the ATM subscriber line concentrator 30 and the call controlfunction 10 c of the network terminator (40: any of 40 a to 40 c), usingan optional PVC (Permanent Virtual Channel) connection channel 210 b asa call control channel. Thus, the establishment and release of the SVCconnection 200 b is controlled between the ATM subscriber lineconcentrator 30 and the network terminator 40.

A call control procedure is executed between the call control function100 c of the network terminator 40 and the call control function 100 dof the subscriber terminal (50: any of 50 a to 50 c), using an optionalPVC connection channel 210 c as a call control channel. Thus, theestablishment and release of the SVC connection 200 c is controlledbetween the network terminator 40 and the subscriber terminal 50.

However, there are the following problems in the conventional callcontrol function described above.

The first problem is in that the network terminators 40 a to 40 c, andthe subscriber terminal 50 a to 50 c are expensive in price. This isbecause the call control function is installed into each of the ATMsubscriber line concentrator 30, the network terminators 40 a to 40 c,and the subscriber terminal 50 a to 50 c. Because the call controlfunctions are different depending upon the units, the development costincreases. Also, because the memory capacity is needed for the callcontrol function, each apparatus becomes expensive. As a result, theinvestment to ATM subscriber network 11 increases.

In the second problem, the maintenance when the specification of thecall control function is updated takes time and effort. This is becausethe call control functions are installed in the ATM subscriber lineconcentrator 30, the network terminators 40 a to 40 c, and thesubscriber terminal 50 a to 50 c. In case of the update of thespecification of the call control function, a software of the callcontrol function of each of the ATM subscriber line concentrators 30,the network terminators 40 a to 40 c, and the subscriber terminal 50 ato 50 c must be updated.

In the third problem, the throughputs of the network terminators 40 a to40 c, and the subscriber terminal 50 a to 50 c are decreased. This isbecause the SSCOP layer contained in the call control protocol needs totransmit and receive an SSCOP layer control ATM cell in the unit ofseveral seconds for the establishment and maintenance of connection in alink layer.

Also, in a substitution call control procedure which is proposed as aproxy signaling agent (to be referred to as PSA hereinafter) in UNI 4.0(ATM Forum Technical Committee ATM UNI Signaling Specification Version4.0), there are two problems. That is, they are where an agent of thesubstitution call control should be installed in the system, and acommunication system between the substitution call control agent and theapplication of the apparatus is not defined.

In conjunction with the above description, an ATM line concentrator isdescribed in Japanese Laid Open Patent application (JP-A-Heisei10-65670). In this reference, transmission path terminating circuit (16)to (18), an ATM switch (19), and a signaling terminating circuit (20)are provided. Information for executing signaling is transmitted throughthe transmission path terminating circuits (16) to (18) using the ATMswitch (19) and the signaling terminating circuit (20). The signaling isa procedure to establish a virtual connection channel between the ATMexchanger (1) and one of the subscriber terminals (5) to (8). At thistime, the transmission path terminating circuit (16) terminates aphysical transmission path (9) which is accommodated by the ATMexchanger (1). Also, the transmission path terminating circuits (17) and(18) terminate physical transmission paths (10) and (11) which arerespectively accommodated by the ATM multiplexers (3) and (4) connectedto the subscriber terminals (5) to (8), for separating and multiplexinginformation. Thus, a wide band service can be effectively provided.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a substitution callcontrol system in which a network terminator and a subscriber terminalare provided with low costs, so that an ATM subscriber network can beconstructed in a low cost.

Another object of the present invention is to provide a substitutioncall control system including an ATM subscriber network in whichmaintainability of a call control function can be improved.

Still another object of the present invention is to provide acommunication system which can be constructed easily as a communicationsystem between a substitution call control function and an application.

One aspect is directed to a call control system including an ATM(Asynchronous Transfer Mode) communication network, the system includesa plurality of network terminators respectively connected with aplurality of subscriber terminals. Additionally, the system includes anATM subscriber line concentrator configured to form VCs (VirtualConnection) with the plurality of network terminators and coupled to anATM switching apparatus of the ATM network through a UNI (User-NetworkInterface). The ATM subscriber line concentrator performs a protocolconversion between an ATM protocol used between the ATM subscriber lineconcentrator and the ATM switching apparatus and a non-ATM protocol usedbetween the ATM subscriber line concentrator and the plurality ofnetwork terminators.

Yet another aspect is directed to an ATM subscriber line concentratorincluding a first communication layer structure, a second communicationlayer structure, and a substitution control component. The firstcommunication layer structure communicates with an ATM switchingapparatus using an ATM protocol. The second communication layerstructure communicates with a plurality of network terminatorsrespectively coupled to a plurality of subscriber terminals using anon-ATM protocol. The substitution control component performs a protocolconversion between the ATM protocol used by the first communicationlayer structure and the non-ATM protocol used by the secondcommunication layer structure.

Yet another aspect is directed to a method of coupling an ATM switchingapparatus and an ATM subscriber line concentrator to network terminatorsand subscriber terminals in an ATM network. The method includescommunicating using an ATM protocol between the ATM switching apparatusand the ATM subscriber line concentrator; converting between the ATMprotocol and a non-ATM protocol at the ATM subscriber line concentrator;and communicating between the network terminators and the subscriberterminals using the non-ATM protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a conventional ATM communicationapparatus;

FIG. 2 is a diagram illustrating an example of protocols for callcontrol functions in the conventional ATM communication apparatus shownin FIG. 1;

FIG. 3 is a block diagram illustrating the structure of a substitutioncall control system according to a first embodiment of the presentinvention;

FIG. 4 is a diagram illustrating a management table used in thesubstitution call control system according to the first embodiment ofthe present invention;

FIG. 5 is a diagram illustrating an example of protocols used in thesubstitution call control system according to the first embodiment ofthe present invention;

FIG. 6 is a diagram format illustrating another example of the protocolof the substitution call control system according to a second embodimentof the present invention;

FIG. 7 is a block diagram illustrating the logical channel structure ofan ATM subscriber network when the protocols of FIG. 5 are used for thesubstitution call control system in the ATM subscriber network of thepresent invention; and

FIG. 8 is a block diagram illustrating the logical channel structure ofthe ATM subscriber network when the protocols of FIG. 6 are used for thesubstitution call control function in the ATM subscriber network of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A substitution call control system in an ATM communication apparatus ofthe present invention will be described below in detail with referenceto the attached drawings.

FIG. 3 is a block diagram illustrating the call control system of an ATMcommunication apparatus of the present invention. In FIG. 3, an ATMsubscriber network 11 is connected with an ATM switching apparatus 20 ofan ATM network 10 through a UNI (User-Network Interface) 12. The ATMsubscriber network 11 is composed of an ATM subscriber line concentrator30, and a plurality of network terminators 40 a to 40 c. The ATMsubscriber line concentrator 30 accommodates the plurality of networkterminators 40 a to 40 c. Each of a plurality of subscriber terminals 50a to 50 c is connected with a corresponding one of the networkterminators 40 a to 40 c.

In the substitution call control system, a call control function 100 ais installed in the ATM switching apparatus 20 of the ATM network 10. Asubstitution call control function 101 is installed in the ATMsubscriber line concentrator 30 in the ATM subscriber network 11. Thesubstitution call control function is proposed in UNI 4.0. The networkterminators 40 a to 40 c in FIG. 3 are not provided with any callcontrol function, unlike the conventional network terminators shown inFIG. 1. Also, the subscriber terminals 50 a to 50 c in FIG. 3 are notprovided with any call control function, unlike the subscriber terminalsshown in FIG. 1.

When a given one of the subscriber terminals 50 a to 50 c issues a callprocessing request to the ATM subscriber line concentrator 30 through acorresponding one of the plurality of network terminators 40 a to 40 c,a line number connected to the given subscriber terminal and an ATMaddress of the given network terminator or subscriber terminal are held.

Also, when one of the plurality of subscriber terminals issues a callprocessing request to the ATM subscriber line concentrator through acorresponding one of the plurality of network terminators, it ispreferable that a call number is held.

In addition, when a SVC (Switched Virtual Channel) connection isestablished in response to a call processing request issued from one ofthe plurality of subscriber terminals to the ATM subscriber lineconcentrator through a corresponding one of the plurality of networkterminators, a VPI (Virtual Path Identifier) value and a VCI (VirtualChannel Identifier) value of the SVC connection are held. That is, thesubstitution call control function holds VPI/VCI values of a SVCconnection when the SVC connection is established based on an ATMaddress for identifying another subscriber terminal, a line number towhich the other subscriber terminal is connected, and a request of SVCconnection establishment/release control.

Also, the network terminators or the subscriber terminal is subjected toIETF (Internet Engineering Task Force) RFC (Request For Comment)1577,classical IP (Internet Protocol) and ARP over ATM (to be referred to asIPOA hereinafter) and contains RFC793, TCP/RFC791, IP or RFC768 UDP/IPprotocol, as to the protocol for the message transmission and receptionfor requesting the control establishment and release of the SVCconnection to the substitution call control function of the ATMsubscriber line concentrator.

Moreover, the network terminators or the subscriber terminal contains xDSL (Digital Subscriber Line, and including Asymmetric DSL,High-bit-rate DSL, Rate-Adaptive DSL, Symmetric DSL, andVery-high-bit-rate DSL) which is being standardized in ADSL Forum as asystem for mapping to an ATM cell a message for requesting the controlof establishment and release of a SVC connection to the substitutioncall control function of the ATM subscriber line concentrator.

In the present invention, any existing protocol and a communicationsystem are used for the message for requesting the control of theestablishment and release of the SVC connection between the substitutioncall control function of the ATM subscriber line concentrator and anapplication of the network terminator and the subscriber terminal. Forthis reason, it is possible to use the SVC connection between the ATMnetwork and the ATM subscriber network through the substitution callcontrol function, when a substitution call control procedure and asubstitution call control message are determined between thesubstitution call control function and the application of each unit.

Also, in the present, a management table is provided such that thesubstitution call control function can manage ATM addresses of thenetwork terminators and the subscriber terminals and SVC connections inthe ATM network. Therefore, it is possible to develop the applicationwithout being conscious of the call control function in the networkterminator and the subscriber terminal.

A channel 210 a (VPI/VPC=0/5), which is defined in UNI 3.1, is providedbetween the ATM subscriber line concentrator 30 and the ATM switchingapparatus 20, for transmission and reception of a call control messagedefined by UNI 3.1 of ATM Forum. The ATM subscriber line concentrator 30is provided with the substitution call control function 101 to controlSVC connections 200 b and 200 c in the ATM subscriber network 11. Thesubstitution call control function 101, the network terminators 40 a to40 c and the subscriber terminals 50 a to 50 c establish PVC connections210 b and 210 c to transmit and receive a substitution call controlmessage.

FIG. 4 is a diagram illustrating the management table 300 of thesubstitution call control function 101 shown in FIG. 3. The data storedin the management table 300 is composed of a line number 301, an ATMaddress 302, a call number 303, a VPI value 304, and a VCI value 305.The line number 301 indicates the number of a line to which eachsubscriber terminal 50 accommodated in the ATM subscriber lineconcentrator 30 is connected. The ATM address 302 is an address of thenetwork terminator 40 or the subscriber terminal 50. The call number 303is allocated when the substitution call control function 101 transmitsand receives a call control message to and from the ATM switchingapparatus 20 instead of the subscriber terminal 50. The VPI 304 and VCI305 values are allocated when the substitution call control function 101transmits and receives the call control message to and from the ATMswitching apparatus 20 instead of the subscriber terminals 50 a to 50 c.

FIG. 5 is a diagram illustrating protocols in the first embodiment ofthe present invention when there is mapped to a TCP/UDP layer, asubstitution call control message which is transmitted or receivedbetween the substitution call control function 101 and the networkterminators 40 a to 40 c or the subscriber terminal 50 a to 50 c. Theaddress for the network terminator 40 is registered as the ATM address302 of the management table 300.

In the UNI 12 between the ATM switching apparatus 20 of the ATM network10 and the ATM subscriber line concentrator 30 of the ATM subscribernetwork 11,

SDH (Synchronous Digital Hierarchy) layers 110 a and 110 b,

ATM layers 111 a and 111 b subject to ITU-T recommendation I.361,

AAL5 layers 112 a and 112 b subject to ITU-T recommendation I.363,

SSCOP (Service Specific Connection Oriented Protocol) layers 113 a and113 b subject to ITU-T recommendation Q. 2110,

SSCF (Service Specific Coordination Function) layers 114 a and 114 bsubject to ITU-T recommendation Q. 2130, and

signaling layers 115 a and 115 b (containing ITU-T recommendation Q2931,ITU-T Q2971, UNI 3.1, and UNI 4.0) are provided as the call controlprotocol, like the conventional apparatus shown in FIG. 1. The layersare controlled by the ATM switching apparatus application 130 and theATM subscriber line concentrator application 140.

The ATM subscriber line concentrator application 140 is provided withthe substitution call control function 101 and the network terminatorsapplication 150. A substitution call control protocol between the ATMsubscriber line concentrator application 140 and the network terminatorapplication 150 include:

SDH/xSDL layers 116 a and 116 b,

ATM layers 111 c and 111 d,

AAL5 layers 112 c and 112 d,

IEEE802.2 LLC/SNAP layers 117 a and 117 b,

IP layers 118 a and 118 b, and

TPC/UPD layers 119 a and 119 b.

The substitution call control protocol is used to transmit and receivethe substitution call control message. When the SDH layer is provided,the system is the IPOA system, and when the xDSL layer is provided, thesystem uses the xDSL over ATM communication system and the IPOA system.

A substitution call control protocol between the network terminatorsapplication 150 and the subscriber terminal application 160 includes:

IEEE802.3 Ether layers 120 a and 120 b,

IEEE802.5 MAC (Media Access Control) layers 121 a and 121 b,

IP layers 118 b and 118 c, and

TPC/UDP layers 119 b and 119 c.

The substitution call control protocol is used to transmit and receivethe substitution call control message.

FIG. 6 is a diagram is illustrating the protocol in the secondembodiment of the present invention when the substitution call controlmessage transmitted and received between the substitution call controlfunction 101 and the network terminators 40 a to 40 c or the subscriberterminal 50 a to 50 c is mapped to an ATM cell.

The UNI 12 between the ATM switching apparatus 20 and the ATM subscriberline concentrator 50 includes:

SDH layers 110 a and 110 b,

ATM layers 111 a and 111 b,

AAL5 layers 112 a and 112 b,

SSCOP layers 113 a and 113 b,

SSCF layers 114 a and 114 b, and

signaling layers 115 a and 115 b

as the call control protocol, like the case of FIG. 5. The UNI 12 iscontrolled by ATM switching apparatus application 130 and the ATMsubscriber line concentrator application 140 with the substitution callcontrol function 101.

The ATM subscriber line concentrator application 140 which is providedwith the substitution call control function 101, and the networkterminators application 150. The substitution call control protocolbetween the ATM subscriber line concentrator application 140 and thenetwork terminator application 150 includes:

SDH/xDSL layers 116 a and 116 b,

ATM layers 111 c and 111 d, and

AAL layers 112 c and 112 d.

The substitution call control protocol is used to transmit and receivethe substitution call control message. When the xDSL layer is provided,the system uses the xDSL over ATM communication system.

A substitution call control protocol between the network terminatorsapplication 150 and terminal application 160 includes:

SDH layers 10 e and 110 f,

ATM layers 111 d and 111 f, and

AAL5 layers 112 d and 112 f.

The substitution call control protocol is used to transmit and receivethe substitution call control message.

The ATM network 10 determine the format of the substitution call controlmessage to be transmitted and received between the substitution callcontrol function 101 of the ATM subscriber line concentrator application140 and the network terminators application 150 and the subscriberterminal application 160, to operate the substitution call controlfunction.

Also, it is determined whether the system of the substitution callcontrol message should be mapped to the TCP/UDP layer shown in FIG. 5 orthe ATM cell shown in FIG. 6, and the ATM subscriber network 11 of FIG.3 is built up.

Further, the line number 301 of the subscriber terminal 50 and the ATMaddress 302 as the ATM address of the network terminator 40 or thesubscriber terminal 50 is set in the management table 300 which ismanaged by the substitution call control function 101 of the ATMsubscriber line concentrator 30.

Next, the operation of the SVC connection establishment and releasecontrol in the ATM network 10 and the ATM subscriber network 11 in FIG.3 will be described.

The ATM switching apparatus application 130 and ATM subscriber lineconcentrator application 140 execute a standard call control procedurethrough the call control channel 210 a (VPI/VCI=0/5) between the ATMswitching apparatus 20 and the ATM subscriber line concentrator 30 toestablish the SVC connection 200 a (VPI/VCY=X/Y).

In the SVC connections 200 b and 200 c between the ATM subscriber lineconcentrator 30 and the network terminator (40: 40 a to 40 c) and thenetwork terminators 40 and the subscriber terminal (50: 50 a to 50 c),the VPI/VCI=X/Y values of the SVC connection 200 a between the ATMswitching apparatus 20 and the ATM subscriber line concentrator 30 areset to a predetermined substitution call control message. These valuesare informed to the network terminator application 150 of the networkterminator 40 and the subscriber terminal application 160 of thesubscriber terminal 50 through the PVC connections 210 b and 210 c(VPI/VCI=0/5, for example) by a predetermined substitution call controlprocedure, such that the VPI/VCI=X/Y values of the SVC connections 200 band 200 c are set.

The call number when the call control procedure with ATM switchingapparatus 20 is executed is stored in the call number column 303 of themanagement table 300 managed by the substitution call control function101.

Also, the value X of the VPI and the value Y of the VCI of the SVCconnection 200 a which has been established between the ATM switchingapparatus 20 and the ATM subscriber line concentrator 30 are set in theVPI column 304 and VCI column 305 of the management table 300 managed bythe substitution call control function 101. Thus, the management table300 is updated.

The ATM switching apparatus application 130 and the ATM subscriber lineconcentrator application 140 execute the standard call control procedurebetween the ATM switching apparatus 20 and the ATM subscriber lineconcentrator 30 to releases the SVC connection 200 a (VPI/VCY-=X/Y).

In the SVC connections 200 b and 200 c between the ATM subscriber lineconcentrator 30 and the network terminator 40 and between the networkterminator 40 and the subscriber terminal 50, when the SVC connection200 a (VPI/VCI=X/Y) between the ATM switching apparatus 20 and the ATMsubscriber line concentrator 30 is released by the standard call controlprocedure through the call control channel 210 a (VPI/VCI=0/5, forexample), the VPI value of X and the VCI value of Y of the released SVCconnection 200 a are set to the predetermined substitution call controlmessage and are notified to the network terminator application 150 ofthe network terminators 40 and the subscriber terminal application 160of the subscriber terminal 50 through the PVC connections 210 b and 210c (VPI/VCI=0/5) by the predetermined substitution call controlprocedure. Thus, the VPI/VCI=X/Y value of the SVC connections 200 b and200 c are released.

In conjunction with the release of the SVC connections 200 b and 200 c,the contents of the management table 300 managed by the substitutioncall control function 101 are updated. That is, the call number 303 ofthe released SVC connection 200 a when the call control procedure withthe ATM switching apparatus 20 is executed is deleted. Also, data of thesame row as the call number in the columns of VPI 304 and VCI 305 aredeleted.

FIG. 7 is a block diagram illustrating the structure of the logicalchannel of the ATM subscriber network 11 when the protocol shown in FIG.5 is used for the substitution call control system in the ATM subscribernetwork 11 of the present invention. In this case, an ATM addressallocated to the network terminator is registered in the managementtable 300. The call control procedure is executed between the ATMswitching apparatus 20 and the ATM subscriber line concentrator 30through call control channel 210 a (VPI/VCI=0/5) which is the PVCconnection defined in UNI 3.1, and the establishment and release of theSVC connections 200 a between the ATM switching apparatus 20 and the ATMsubscriber line concentrator 30 is controlled.

The predetermined substitution call control procedure is executedbetween the ATM subscriber line concentrator 30 and the networkterminator 40, using the call control channel 210 b (VPI/VCI=0/5) (thevalues of VPI/VCI are same as those of the channel 210 a) which is thePVC connection defined in UNI 3.1, and the establishment and release ofthe SVC connection 200 b between the ATM subscriber line concentrator 30and the network terminators 40 a to 40 c are controlled.

The network terminators 40 and the subscriber terminal 50 are connectedby an ether net 220 so that the predetermined substitution call controlprocedure is executed. A connection corresponding to the SVC connections200 a or 200 b between the ATM switching apparatus 20 and the ATMsubscriber line concentrator 30 or between the ATM subscriber lineconcentrator 30 and the network terminators 40 is established andreleased on the ether net 220.

FIG. 8 is a block diagram illustrating the structure of the logicalchannel of the ATM subscriber network 11 when the protocol shown in FIG.6 is used to the substitution call control system of the presentinvention in the ATM subscriber network 11. In this case, an ATM addressof the subscriber terminal is registered in the management table 300.

The call control procedure is executed between the ATM switchingapparatus 20 and the ATM subscriber line concentrator 30 through thecall control channel 210 a (VPI/VCI=0/5) which is the PVC connectiondefined in UNI 3.1, and the establishment and release of the SVCconnection 200 a between the ATM switching apparatus 20 and the ATMsubscriber line concentrator 30 is controlled.

The predetermined substitution call control procedure is executedbetween the ATM subscriber line concentrator 30 and the networkterminator 40, using the call control channel 210 b (VPI/VCI=0/5,recommended as an example) (the values of VPI/VCI are the same as thoseof the channel 210 a), and the establishment and release of the SVCconnection 200 b between the ATM subscriber line concentrator 30 and thenetwork terminator 40 are controlled.

Also, the predetermined substitution call control procedure is executedbetween the network terminator 40 and the subscriber terminal 50, usingthe call control channel 210 c (VPI/VCI=0/5, recommended as the example)(the values of VPI/VCI are the same as those of the channel 210 a), andthe establishment and release of the SVC connection 200 c between thenetwork terminator 40 and the subscriber terminal 50 are controlled.

As described above, according to the present invention, a networkterminator and a subscriber terminal can be provided in a low cost. Thisis because in the ATM subscriber network 11, the substitution callcontrol function 101 is installed only in the ATM subscriber lineconcentrator 30, and it is not necessity to install the standard callcontrol function in the network terminators and the subscriberterminals. Therefore, the development expenses of the call controlfunction for these units becomes unnecessary, and the memory quantityfor these call control functions can be reduced.

As the communication system between the subscriber terminal and thenetwork terminator, the existing protocol is used for the substitutioncall control function. Therefore, if the substitution call controlprocedure and the substitution call control message format are defined,the substitution call control function is possible to be used.

It is possible to reduce the investment expense for the ATM subscribernetwork. This is because the number of network terminators and thesubscriber terminals contained in the ATM subscriber network isenormous. Because these unit prices are low so that the price reductioncan be attained as the whole ATM subscriber network.

Also, the maintenance of the ATM subscriber network becomes easy. Thisis, only the ATM subscriber line concentrator needs to be maintained forthe call control protocol of the ATM network.

Also, even in the subscriber terminal in which an adapter for theEthernet is installed, it is possible to easily use the SVC connectionof the ATM network. In the ATM subscriber line concentrator and thesubscriber terminal, it is sufficient to install a simple dedicateddriver for the substitution call control function procedure because thesubstitution call control message is mapped onto the TPC/IPcommunication and the UDP/IP communication.

1. A call control system in a communication network, the systemcomprising: a plurality of network terminators to respectively connectto a plurality of subscriber terminals; and a subscriber lineconcentrator to establish and terminate, using a call control function,VCs (Virtual Connections) with the plurality of network terminators andcouple to a switching apparatus of the network through a UNI(User-Network Interface), where the subscriber line concentratorperforms a protocol conversion between a first protocol stack usedbetween the subscriber line concentrator and the switching apparatus anda second protocol stack used between the subscriber line concentratorand the plurality of network terminators, where the plurality of networkterminators performs a protocol conversion between the second protocolstack and a third protocol stack used between the plurality of networkterminators and the plurality of subscriber terminals, where the firstprotocol stack differs from the second protocol stack and the secondprotocol stack differs from the third protocol stack, and where at leastone layer of the first, second, and third protocol stacks uses a sameprotocol.
 2. The system of claim 1, where the at least one layercomprises two or more different layers.
 3. The system of claim 1, wherethe plurality of network terminators and the plurality of subscriberterminals are connected by a PVC (permanent virtual circuit).
 4. Thesystem of claim 1, where the subscriber line concentrator and theplurality of network terminators are connected by a PVC (permanentvirtual circuit).
 5. The system of claim 4, where a virtual pathidentifier (VPI)/virtual channel identifier (VCI) value of the permanentvirtual circuit is 0/5.
 6. The system of claim 1, where the subscriberline concentrator communicates with the plurality of network terminatorsand the plurality of subscriber terminals using a substitute callcontrol message that is transmitted and received using the secondprotocol stack.
 7. The system of claim 6, where the substitute callcontrol message is transmitted and received with subscriber data.
 8. Thesystem of claim 6, where the substitute call control message istransmitted and received via an IP (Internet Protocol) and an ARP(Address Resolution Protocol) over ATM (asynchronous transfer mode). 9.The system of claim 6, where the substitute call control message istransmitted and received by a DSL (Digital Subscriber Line) over ATM(asynchronous transfer mode).
 10. The system of claim 1, where theplurality of network terminators and the plurality of subscriberterminals are not provided with call control functions.
 11. A method ofcoupling a network switching apparatus and a subscriber lineconcentrator to network terminators and subscriber terminals in asubscriber communication network, the method comprising: communicating,using a first protocol stack, between the network switching apparatusand the subscriber line concentrator; converting between the firstprotocol stack and a second protocol stack at the subscriber lineconcentrator; communicating, using the second protocol stack, betweenthe network terminators and the subscriber line concentrator, where thefirst protocol stack and the second protocol stack differ; convertingbetween the second protocol stack and a third protocol stack at thesubscriber network terminators, where the second protocol stack differsfrom the third protocol stack; and communicating, using the thirdprotocol stack, between the network terminators and the subscriberterminals, where at least one layer of the first, second, and thirdprotocol stacks uses a same protocol.
 12. The method of claim 11, wherethe network terminators and the subscriber terminals do not have callcontrol functions.